Short-arch discharge lamp with reflection mirror

ABSTRACT

To meet the requirements of the miniaturization of an apparatus and the enhancement of the efficiency of optical characteristics of an apparatus as a light source apparatus for a mobile liquid crystal projector.  
     A short arc discharge lamp( 11 ) with a reflecting mirror is composed of: a glass reflecting mirror( 1 ) formed by molding, the reflecting mirror( 1 ) having a reflective surface formed in conformity with an even-order function on the inner surface of the reflecting mirror( 1 ); and a short arc discharge lamp( 11 ) sealing a pair of electrodes( 12   a   , 12   b ) therein, the discharge lamp( 11 ) having sealing portions( 14   a   , 14   b ) formed on both ends thereof and a base( 15 ) fixed to the sealing portion( 14   b ), one of the sealing portions( 14   a   , 14   b ); wherein: the discharge lamp( 11 ) is disposed so as to agree with the optical axis of the reflecting mirror( 1 ); the base is fixed in an insertion aperture of a hollow neck-shaped portion( 4 ) formed at the center of the bottom portion of the reflecting mirror( 1 ); the discharge lamp( 1 ) is characterized in that  
     a part of said inner surface of said insertion aperture( 3 ) of said hollow neck-shaped portion near said base is worked into a cylindrical portion( 4   c ), the narrowest portion( 4   b ) is formed from the cylindrical portion( 4   c ) toward a reflective surface, and a portion continuing, while widening, from the narrowest portion( 4   b ) toward said reflective surface is formed by a molding surface( 4   a ).

TECHNICAL FIELD OF USE

[0001] The present invention relates to a light source apparatus to be used as a back light of a liquid crystal projection apparatus, in particular to an improvement of a glass reflecting mirror.

BACKGROUND ART

[0002] Recently, a short arc discharge lamp has rapidly been spreading as a light source of a liquid crystal projector. Such a kind of lamp is used as a light source apparatus constructed by combining with a reflecting mirror having a reflective surface formed on the internal surface of the reflecting mirror as a paraboloid of revolution or an ellipsoid of revolution for collecting light to a liquid crystal panel. Moreover, such a light source apparatus is required to be more miniaturized and to have a higher efficiency as a light source apparatus for a mobile projector. Accordingly, various proposals for the downsizing of the light source apparatus and for utilizing the reflective surface of a reflecting mirror efficiently have been made.

[0003] A unit of an electric bulb and a reflector shown in Japanese Patent Laid-Open Publication No. Hei 6-203806 has been disclosed as one of the above-mentioned proposals The reflector 31 of the unit forms a hollow neck-shaped portion 32 at the bottom portion of the reflector 31 at the time of working a glass reflecting mirror as shown in FIGS. 3-5. For making an electric bulb insertion aperture 33 small and for making a reflective surface 31 a large, post-working for forming the electric bulb insertion aperture 33 is performed with a grindstone or the like after molding (FIG. 3). Consequently, when the reflector 31 is used as a unit, the unit causes the problem in which the surface of the electric bulb insertion aperture, which is the end face of the hollow neck-shaped portion, cracks to be broken owing to the heat during the lighting of the electric bulb, since the surface is injured by the grindstone. Moreover, in the case where an adhesive agent for fixing an electric bulb (cement) is filled in the hollow neck-shaped portion, the unit causes the problem in which the surface is more easily broken owing to the thermal stress caused by the difference of the coefficients of thermal expansion of the glass and the adhesive agent.

[0004] Moreover, as shown in FIG. 5, the reflector 31 and the electric bulb 41 are arranged so that the central axis of the reflector and the optical axis of the electric bulb agree with each other. Then, the adhesive agent 51 is filled into the inside of the hollow neck-shaped portion 32 to fix the reflector 31 and the electric bulb 41. Thus, the unit is assembled. However, because a base 43 with a screw to be fixed to a sealing portion 42 of the electric bulb 41 at the time of assembling is disposed on a tapered portion 32 a on the inner surface of the hollow neck-shaped portion 32, it is difficult to adjust the positions of the electric bulb and the reflector when the positions of the electrodes sealed on the central axis of the electric bulb are dispersed at the time of manufacturing the electric bulb. Consequently, there is the problem of producing an inferior good.

[0005] A countermeasure of this problem is to separate the base 43 from the reflective surface 31 a of the reflector 31 on a large scale lest a cylinder portion 43 a of the base 43 should be contacted with a narrow portion 32 b on the reflective surface 31 a side of the tapered portion 32 a of the hollow neck-shaped portion 32 at the time of adjusting the optical axes of the bulb and the reflector. After that, the bulb and the reflector are fixed with the adhesive agent 51. Incidentally, a reference numeral 52 in the figure designates a ring-shaped glass member for preventing the outflow of the adhesive agent. However, even if the electric bulb 41 is fixed by the use of the adhesive agent after the positional adjustment, at the time of fixing a lug terminal for power supply by utilizing a screw 43 b formed on an end of the cylinder portion 43 a of the base, only the base is rotated while the sealing portion of the electric bulb is fixed with the adhesive agent since the base is fixed in the neck-shaped portion of the reflector only in a shallow depth. Consequently, the countermeasure has the defect that the electric bulb is thus broken.

[0006] The present invention was made in view of the above description. The invention can meet the miniaturization of an apparatus and the enhancement of the efficiency of optical characteristics, both being required as a light source apparatus for a mobile liquid crystal projector. Moreover, the invention aims to provide a short arc discharge lamp with a reflecting mirror which can prevent the generation of cracks from the end surface of the neck-shaped portion of the reflecting mirror owing to heat generation from the discharge lamp accompanied by the miniaturization, and which can adjust the positions of the reflecting mirror and the lamp even if the lamp deviates from the center axis of the electrode axis at the time of manufacturing the lamp, and further which has a long life and superior optical characteristics.

DISCLOSURE OF THE INVENTION

[0007] For achieving the above-mentioned object, a short arc discharge lamp with a reflecting mirror according to the present invention includes: a glass reflecting mirror formed by molding, the reflecting mirror having a reflective surface formed in conformity with an even-order function on the inner surface of the reflecting mirror; and a short arc discharge lamp sealing a pair of electrodes therein, the discharge lamp having sealing portions formed on both ends thereof and a base fixed to one of the sealing portions; wherein: the discharge lamp is disposed so as to agree with the optical axis of the reflecting mirror; the base is fixed in an insertion aperture of a hollow neck-shaped portion formed at the center of the bottom portion of the reflecting mirror; the discharge lamp is characterized in that a part of said inner surface of said insertion aperture of said hollow neck-shaped portion near said base is worked into a cylindrical portion, the narrowest portion is formed from the cylindrical portion toward a reflective surface, and a portion continuing, while widening, from the narrowest portion toward said reflective surface is formed by a molding surface.

BRIEF EXPLANATION OF THE DRAWINGS

[0008]FIG. 1 is a sectional view of an embodiment according to the present invention. FIG. 2 is an enlarged sectional view of the main part of the embodiment of FIG. 1. FIG. 3 is an explanatory view showing a state of a conventional reflector after molding. FIG. 4 is an explanatory view showing a post-working state of the conventional reflector. FIG. 5 is a sectional view of the main part of the conventional unit of the reflector and an electric bulb.

BEST MODE FOR PRACTICING THE INVENTION

[0009] In the following, a preferred embodiment will be described on the basis of the attached drawings. FIGS. 1 and 2 are a sectional view and an enlarged sectional view of the main part, respectively, of a short arc discharge lamp according to the embodiment of the present invention. A reference numeral 1 in the figures designates a reflecting mirror made of hard glass (the expansion coefficient thereof is 38×10⁻⁷ cm/° C.). The reflecting mirror 1 has a reflective surface 1 a shaped in a paraboloid of revolution on its inner surface. An aperture portion 2 is formed on one side of the reflecting mirror. A neck-shaped portion 4 having an insertion aperture 3 is formed at the center of the bottom portion on the other side of the reflecting mirror. In the figure, a reference numeral 11 designates a short arc discharge lamp made of silica arc tube. The discharge lamp 11 seals a pair of electrodes 12 a, 12 b along the optical axis of the discharge lamp 11. A luminous material such as mercury or the like is sealed in the discharge lamp 11 together with a starting gas. Moreover, arc tube sealing portions 14 a, 14 b, in which molybdenum foils 13 a, 13 b are embedded, are formed on both ends of the luminous portion. Moreover, a base 15 with a screw is fixed on the sealing portion 14 b, one of the sealing portions 14 a, 14 b. The base 15 is composed of a cylinder portion 15 a and a screw portion 15 b on the end of the cylinder portion 15 a.

[0010] The above-mentioned reflecting mirror 1 having a focal distance of 6 mm and the discharge lamp 11 are arranged so that the center axis of the reflecting mirror and the optical axis of the lamp agree with each other. The base 15 with the screw fixed at the arc tube sealing portion 14 b of the discharge lamp 11 is inserted into the insertion aperture 3 formed in the neck-shaped portion 4 of the reflecting mirror 1, and the base 15 is fixed with an adhesive agent 21.

[0011] On the inner surface of the neck-shaped portion 4 of the reflecting mirror 1 according to the present invention, a portion (an inlet portion of the insertion aperture) which is continued with widening from the insertion aperture 3 of the neck-shaped portion 4 toward the reflecting surface is formed by a molding surface 4 a.

[0012] Because the molding surface 4 a keeps the surface when it was formed and it does not need a cutting working after press molding with a metal mold, it has not any scars quite at all to be a smooth surface.

[0013] Moreover, the narrowest portion 4 b of the insertion aperture 3 is formed at a portion continuing to said molding surface 4 a for preventing the outflow of the adhesive agent 21 to the molding surface 4 a when the adhesive agent 21 is poured into the neck-shaped portion 4 after assembling.

[0014] Moreover, the portion ranging from the narrowest portion 4 b of the insertion aperture 3 to the external end portion thereof is formed to be a cylinder 4 c. The cylinder 4 c is formed to have a large diameter for enabling the insertion of the cylinder portion 15 a of the base 15 with the screw fixed to the arc tube sealing portion 14 b, which is to be inserted into the insertion aperture 3 of the neck-shaped portion 4, with a sufficient margin, and for enabling the positional adjustment of the pair of the electrodes to agree with the center axis of the reflecting mirror with a sufficient margin in case of the axial deviation of the pair of the electrodes which may happen at the time of manufacturing the lamp. Incidentally, in the case where the shape of the cross section of the cylindrical portion of the base to be inserted into the insertion aperture is a hexagon for making it difficult to turn around after fixing, similar effects can be obtained.

[0015] Owing to the structure, even if the temperature around the light source apparatus used in a liquid crystal projector is set to be high with the aim of downsizing of the light source apparatus, there is no chance that cracks are produced from the glass working portion on the inner surface of the neck-shaped portion of a reflecting mirror as in the prior art, and the life characteristic can be improved. For example, in case of an apparatus to be used at a horizontal position, a position where the temperature of the reflecting mirror is highest is a position H in FIG. 1. Although the temperature of the position H of the conventional reflecting mirror is about 480° C. and the distortion temperature of glass is 520° C., the conventional reflecting mirror cracks from the periphery of the portion worked by cutting after repeating lighting. On the other hand, the reflecting mirror according to the present invention has no portion worked by cutting in the molding surface of the neck-shaped portion, and then the surface portion does not become a high temperature portion. Consequently, even if the glass having the same composition is used and the temperature of the molding surface becomes about 500° C. at the time of lighting, no cracks are produced during the life period of the lamp.

[0016] Moreover, the reflecting mirror and the lamp are fixed to each other with an adhesive agent, the main components of which are silica and alumina, after their positional adjustment. The adhesive agent is poured from a notched portion formed in the bottom portion of the neck-shaped portion 4 of the reflecting mirror as the inlet of the adhesive agent. However, because the outflow of the adhesive agent is prevented by the narrowest portion 4 b, the adhesive agent does not flow into the moling surface 4 a and on the reflective surface 1 a. And, the generation of cracks caused by a stress generated by the difference of thermal expansion of the glass reflecting mirror and the adhesive agent can be prevented.

INDUSTRIAL APPLICABILITY

[0017] As described above, a short arc discharge lamp with a reflecting mirror according to the present invention improves the structure and the shape of the neck-shaped portion at the bottom portion of the reflecting mirror, and does not perform cutting working of the surface near the luminous portion of the lamp being a heat generation source. Accordingly, the end surface of the lamp insertion aperture adjoining to the reflective surface is left to be an molding surface as it is, and the periphery portion of the insertion aperture enclosing the base with a screw of the lamp is formed to be a cylindrical portion having the same shape of the cylinder portion of the base. Then, by making the diameter to be sufficiently large, the adjustment of the optical axes of the reflecting mirror and the lamp can sufficiently be performed even if the lamps are dispersed in manufacturing. Moreover, by forming the narrowest portion to be a partition between the cylindrical portion and the molding surface of the insertion aperture, the adhesive agent does not flow into the reflective surface side during operations, and cracks are not produced even if the temperature of the lamp becomes high during its life. Consequently, a short arc discharge lamp with a reflecting mirror having superior optical efficiency can be obtained. 

1. A short arc discharge lamp with a reflecting mirror including: a glass reflecting mirror formed by molding, said reflecting mirror having a reflective surface formed in conformity with an even-order function on an inner surface of said reflecting mirror; and a short arc discharge lamp sealing a pair of electrodes therein, said discharge lamp having sealing portions formed on both ends thereof and a base fixed to one of said sealing portions; wherein: said discharge lamp is disposed so as to agree with an optical axis of said reflecting mirror; and said base is fixed in an insertion aperture of a hollow neck-shaped portion formed at a center of a bottom portion of said reflecting mirror; said discharge lamp characterized in that: a part of said inner surface of said insertion aperture of said hollow neck-shaped portion near said base is worked into a cylindrical portion, the narrowest portion is formed from the cylindrical portion toward a reflective surface, and a portion continuing, while widening, from the narrowest portion toward said reflective surface is formed by a molding surface.
 2. The short arc discharge lamp with a reflecting mirror according to claim 1, said discharge lamp characterized in that said base of said discharge lamp is inserted into the cylindrical portion formed in said insertion aperture of said hollow neck-shaped portion of said reflecting mirror in a state capable of adjusting a position of said base freely; and said base is fixed in said insertion aperture of said neck-shaped portion in a manner of preventing an inflow of an adhesive agent into the molding surface by preventing an outflow of said adhesive agent with the narrowest portion when said adhesive agent is poured into said insertion aperture of said neck-shaped portion. 